We propose a series of clinical trials in the management and prevention of arterial and venous thromboembolism including investigations into pathophysiology and the pharmocology of new anti-thrombotic drugs. The trials included 1). Assessment of intermittent external pneumatic compression of the legs to prevent pulmonary embolism in urologic patients. 2). Evaluation in neurosurgical patients of a hemodynamically optimized system of external pneumatic compression to prevent venous thromboembolism. 3). Investigation in full dose therapy of established thromboembolism of a low molecular weight heparin fraction with limited antithrombin activity but potent anti Xa activity in fractures of the hip. 4). Examination of safety and efficacy of a new radiographic contrast agent in phlebography. 5). Investigation of an inhibitor of thromboxane synthesis in long term patency of arterial by-pass grafts.